A toner binder for electrophotography used for a heat fixing system, which is a fixing system of images commonly applied in copiers, printers and the like, is required to make a toner not fusing to a hot roller even at a high fixing temperature (anti-hot offset property), to be capable of fixing a toner even at a low fixing temperature (low temperature fixability), to have an appropriate impact strength to be used in the form of microparticles, and the like. In order to satisfy these basic required performances, it has been known to use a polyester resin having a constituent unit of an alcoholic compound derived from a bisphenol (for example, refer to U.S. Pat. No. 4,939,059).
In recent years, concerns on durability of copiers and printers using a heat fixing system have been increased. And it has come to be strongly desired to form a stable image even after repeatedly using copiers and the like over a long period of time.
However, when using a conventional toner binder or toner which comprises a polyester resin, there is a problem that long-term running ability is not sufficient.